Drilling bit for drilling while running casing

ABSTRACT

A drill bit for drilling casing in a well bore. The drill bit is constructed from a combination of relatively soft and relatively hard materials. The proportions of the materials are selected such that the drill bit provides suitable cutting and boring of the well bore while being able to be drilled through by a subsequent drill bit. Methods of applying hard materials to a soft material body are provided.

[0001] The present invention relates to drilling tools as are typicallyused for drilling well bores.

[0002] Conventionally, when drilling a well bore of the type used in oilor gas production, a string of drill pipe having a drill bit on thelower end thereof is advanced into the ground. As the drill is advancedinto the ground it encounters different rock formations, some of whichmay be unstable. To minimise problems which may be incurred by runningthe drill bit from one formation to another, it is common practice torun the drill bit to a predetermined depth, and then remove or “trip”the drill string from the bore. Structural casing, typically made ofheavy steel piping, is then lowered into the bore and cemented in placewhen set. The casing acts as a lining within the bore, and preventscollapse of the newly drilled bore or contamination of the oil or gasreservoir.

[0003] As a consequences of having to carry out the above procedure, thecost and time taken to drill a bore is increased as it is necessary toperform a number of trips down the well. It will be appreciated that atthe considerable depths reached during oil and gas production the timetaken to implement complex retrieval procedures to recover the drillstring can be very long, and accordingly the beginning of profitableproduction can be greatly delayed.

[0004] An attempt has been made to mitigate this problem with theintroduction of a procedure known as “drilling with casing”. Thisprocedure relies on the attachment of a drill bit to the actual casingstring, so that the drill bit functions not only to drill the earthformation, but also to guide the casing into the well bore. This isadvantageous as the casing is pulled into the bore by the drill bit, andtherefore negates the requirement of having to retrieve the drill stringand drill bit after reaching a target depth to allow cementing.

[0005] While this procedure greatly increases the efficiency of thedrilling procedure, a further problem is encountered when the casing iscemented upon reaching the desired depth. The advantage of drilling withcasing is that the drill bit does not have to be retrieved from the wellbore. However as a result, should drilling to a greater depth berequired after cementing the casing, the subsequent drill bit has topass through the previous bit in order to advance. This is extremelydifficult as drill bits are required to remove hard rock material andare accordingly very resistant and robust structures typicallymanufactured from materials such as Tungsten Carbide or steel.Attempting to drill through an old drill bit may result in damaging thenew drill bit, adversely affecting the efficiency of any furtherdrilling. Consequently, the damaged drill bit would have to be retrievedfrom the bore and replaced, and the time and cost advantage gained byusing the drilling with casing procedure would be lost.

[0006] It would therefore be a distinct advantage to provide a drill bitfor use during drilling with casing which can drill rock and earthformations but which can also be drilled through by another drill bit.The provision of a drill bit which allows the passage of a subsequentdrill bit through it, would reduce the number of trips into a well borerequired during a normal drilling procedure and minimise the risk ofdamaging any further drill bits introduced into the bore.

[0007] In our prior Patent Application PCT/GB99/01816 we have suggestedthat the drill bit has hard drilling material that may be moved awayfrom the remaining body of the drill shoe prior to subsequent drillingthrough of the drill bit. We have also proposed EP0815342, a drill bitor shoe having hard drilling material placed only on the drill shoe orbit at the peripheral circumference thereof, and specifically only atthe sides of the drill bit or shoe where the diameter is greater thanthe internal diameter of the casing. The present invention isdistinguished from both of these teachings in that it provides for adrill shoe or bit that has hard material within the area below theinternal boundaries of the casing, and does not require moving parts tobe displaced before subsequent drilling through can be commenced.

[0008] It is an object of the present invention to provide a drill bitfor use in a well bore which can drill earth and rock formations andguide a casing string into a well bore simultaneously.

[0009] It is a further object of the present invention to provide adrill bit for use in a well bore which is constructed from a materialwhich allows a second drill bit to drill through it.

[0010] It is a yet further object of the present invention to provide adrill bit for use in a well bore which allows a second drill bit todrill through it, such that the second drill bit is not damaged and canprogress beyond the point reached by the original drill bit within thewell bore.

[0011] According to a first aspect of the present invention there isprovided a drill bit for drilling with casing in a well bore, said drillbit being constructed from a combination of a relatively soft materialand a relatively hard material, wherein the hard material is suitablefor cutting earth or rock, and wherein the combination of materials isin such proportion and in such arrangement to allow a subsequent furtherdrill bit to drill through it.

[0012] Preferably the drill bit is substantially constructed from therelatively soft material, wherein the relatively soft material isadapted to be drilled through with a standard earth drill bit.

[0013] Preferably the drill bit is formed with a body having or beingassociated with a nose portion upon which are cutting members, whereinthe body is made substantially from the relatively soft material and atleast the leading edge or cutting surface of each cutting member is madefrom the hard material.

[0014] Preferably the hard wearing material is a hard material such astungsten carbide or a superhard material such as diamond composite orcubic boron nitride although any other suitable material may be used.

[0015] Preferably the soft, drillable material is aluminium.Alternatively the soft drillable material is copper or brass alloy,although any other suitable material could be used.

[0016] There may be a plurality of soft materials and there may be aplurality of hard materials.

[0017] In one possible embodiment the nose is directly coated with thehard wearing material.

[0018] Optionally the coating is a continuous layer or film that coversthe surface of the nose.

[0019] Alternatively the coating is non-continuous, such that the noseis afforded areas which are not coated by the hard wearing material,wherein upon rotation of the drill bit the cumulative effect of thecoated areas gives complete circumferential coverage of the dimensionsof the drilled hole.

[0020] Alternatively the coating may be applied to an intermediate whichis amenable to the nose of the drill bit.

[0021] Preferably the intermediate is nickel.

[0022] The intermediate may be attached to the nose prior to coatingwith the hard wearing material. Optionally the intermediate may becoated with the hard wearing material prior to attachment to the nose.

[0023] In a second embodiment the hard wearing material is applied tothe nose in the form of preformed elements wherein the cumulative effectof said preformed elements is to cover the surface of the nose and soact as a coating thereof.

[0024] The preformed elements may be chips or fragments of the hardmaterial.

[0025] The preformed elements of the hard material may be directlyapplied to the nose.

[0026] Alternatively the preformed elements of hard material are appliedto the nose following the application of an amenable intermediatematerial to the nose or the preformed elements.

[0027] Preferably the amenable intermediate material is nickelsubstrate.

[0028] The preformed elements may be attached to the nose by standardtechniques such as brazing, welding or shrink fitting.

[0029] Optionally the preformed elements have a re-enforced structure toaid drilling of hard formations. Where the preformed elements have are-enforced structure, preferably the preformed elements arepre-weakened prior to attachment to the nose in order to allow fractureof the preformed elements upon drilling.

[0030] Preferably the drill bit may also comprise a plurality of flowports to allow fluid bypass and lubrication of the bit.

[0031] Preferably the drill bit also comprises a stabiliser orcentraliser.

[0032] Preferably the drill bit also comprises reaming members.

[0033] According to a third aspect of the present invention there isprovided a method of fixing a hard or super hard wearing material to adrill bit nose made of a soft drillable material, wherein a jet is usedto blow gases at very high speeds towards a cast of the nose andparticles of the hard or superhard wearing material are introduced intothe gas stream, wherein the kinetic energy of the procedure is convertedto thermal energy which welds the particles to the nose.

[0034] According to a fourth aspect of the present invention there isprovided a method for fixing a hard or superhard wearing material to adrill bit nose made of a soft drillable material, wherein particles ofthe hard or superhard wearing material are placed within a mould andthereafter the soft drillable material is poured in molten form into themould, such that on cooling said hard or superhard wearing particles areset in situ.

[0035] Alternatively the hard wearing material can be fixed to the noseby a standard technique such as brazing, welding and electroplating.

[0036] In order to provide a better understanding of the invention,example embodiments of the invention will now be illustrated withreference to the following Figures in which;

[0037]FIG. 1 illustrates a drill bit in accordance with the presentinvention;

[0038]FIG. 2 is an elevated view of the top of the drill bit;

[0039]FIG. 3 illustrates an individual cutting member isolated from thedrill bit.

[0040]FIG. 4 illustrates an elevated view of the top of an alternativeembodiment of a drill bit in accordance with the present invention; and

[0041]FIG. 5 illustrates a pre-formed element for attaching to the noseportion of a drill bit.

[0042] Referring firstly to FIG. 1, a drill bit generally depicted at 1,is comprised of a cylindrical body 2, that can be mounted on the lowerend of a casing string (not shown) via a thread end connection 3 thatcan mate with the casing. The drill bit 1 is further comprised of aplurality of cutting members 4 which are fixed to the opposite end ofthe body 2 to the thread end connection 3, namely the nose end 5. Thecutting members 4 extend out from the nose end 5.

[0043] The nose 5 and cutting members 4 are constructed from a materialsuch as aluminium, copper or brass alloy which is soft enough to allowthe aforementioned nose 5 and members 4 to be drilled through by asecond and subsequent drill bit (not shown). The cutting members 4 aresubstantially covered by a relatively hard material 6 typically being ahard material such as tungsten carbide or a superhard material such asdiamond composite or cubic boron nitride. In the depicted embodiment therelatively hard material 6 is located at the “leading edge” of thecutting member 4. In this respect the “leading edge” refers to the sideof the cutting member 4 which directly contacts the ground or rock uponrotation of the drill bit 1. It is recognised that whilst in thedepicted embodiments the hard wearing material is afforded to theleading edge of one or more cutting members 4 on the drill bit 1, theinvention is not limited to this configuration. For example the hardwearing material may be applied to the nose 5 in an embodiment having nocutting members 4 or may be applied to the whole surface of the cuttingmembers 4.

[0044] The relatively hard material 6 may be applied to the cuttingmembers 4 or nose 5 as a coating, that is as a layer or film. In oneembodiment a continuous layer of the material 6 may cover the entiresurface of the nose 5, or the cutting members 4. Alternatively anon-continuous layer of the material may coat the nose 5 or cuttingmembers 4. In this instance, the surface of the nose 5 or cuttingmembers 4 will comprise areas that are not coated. However, uponrotation of the drill bit 1, the cumulative effect of the coated areaswill be complete circumferential coverage of the inside diameter of thecasing in which the drill bit is located.

[0045] It is recognised in the present invention that direct applicationof some coatings to the nose material may not be practical. For example,extremely hard tungsten carbide particles cannot be applied to thepreferred nose materials (e.g. aluminium or copper) by lasercarbwelding. This material can be applied to soft nickel, however machiningsaid drill bit 1 entirely from nickel would be unduly expensive.Therefore in an alternative embodiment, a coating of the hard material 6is applied to an intermediate, typically being nickel substrate, whichis then attached to the nose 5 of the drill bit 1. Alternatively thenickel substrate can be attached to the nose 5 prior to coating.

[0046] In a further embodiment preformed elements of the hard orsuperhard material 6 are applied to the nose 5 or cutting members 4 ofthe drill bit 1 in place of a coating of film. Said preformed elementsmay be chips, or fragments of the hard material 6. Typically theculmative effect of the preformed elements is to cover the surface ofthe nose 5 or the cutting members 4 and so act as a coating thereof. Thepreformed elements may be directly applied to the nose 5 or cuttingmembers 4 or may be applied after applying an amenable material eitherto the nose 5 or cutting members 4 or the preformed element itself. Theamenable material is typically nickel substrate.

[0047] The layout of cutting members 4 can be seen more clearly in FIG.2 which shows the nose end 5, viewed from above, and in FIG. 3 whichshows an individual cutting member 4. It can be seen in FIG. 3 that thecutting means 6 has teeth formations 10 which allow any “chips” ofmaterial remaining in the well bore to pass through the blade structure.

[0048] The nose 5 further comprises flow by areas 7 that allow fluidcirculated within the well bore to lubricate the surfaces of the bit 1.The body 2 also comprises a stabiliser or centraliser 9 which maintainsthe drill bit in the centre of the well bore, and reaming members 8,which function to remove any irregularities or obstructions from thewall of the bore.

[0049] In use, the drill bit 1, is run into a well bore (not shown) fromthe surface, typically whilst being rotated. The drill bit 1 pulls acasing string (not shown) as it is advanced into the newly formed wellbore to a predetermined depth. Upon reaching this depth, the casing iscemented to strengthen the lining of the bore. If drilling beyond thisfirst assembly is required, a second drill bit of a smaller diameter tothe first is run into the well inside the casing string from thesurface.

[0050] Upon reaching the first assembly, the new drill bit can drillthrough the soft drillable material of the original drill bit 1 andcutting members 4, and therefore can proceed to a point beyond the depthreached by the original drill bit 1 within the well bore. The hard orsuper hard material 6 fixed to the cutting members 4 of the originaldrill bit 1 disintegrate into shavings when drilled. The shavingsreleased into the well bore when the original bit 1 is drilled throughdo not obstruct the bore and are therefore not detrimental to thesubsequent drilling process. In this manner a further section of thebore can be drilled beyond the previously attained depth without damageto the new drill bit and without needing to retrieve the first assemblyfrom the bore.

[0051] When used for drilling through harder formations a thickersection of the preformed element will be required. However it will beappreciated that in such an instance, said preformed elements would notbe drillable. Thereby in the event that a thicker element is required,said element is typically pre-weakened prior to attachment to the nose 5or cutting members 4. In this manner, the elements will have theattributes of high stiffness whilst drilling but low resistance tofracture whilst being drilled. The preformed elements can then beapplied directly to the nose 5 or cutting members 4 by brazing orshrink-fitting or could be attached to an amenable material, typicallynickel substrate.

[0052] A first method for fixing the hard or superhard material 6 is nowoutlined. A jet is used to blow gases at very high speeds towards a castor block of the cutting member 4 or nose 5, and which is made from thesoft, drillable material. Typically a speed in the region of Mach 2 isused. Very fine particles of the hard or superhard wearing material areintroduced into the gas stream. The resulting kinetic energy isconverted to thermal energy in the particles, and accordingly the heatedparticles “weld” to the leading edge of the cast or block thereforeforming a thin layer or film.

[0053] It will be appreciated that the abovedescribed method could beused with particles of the hard or superhard material, or withintermediates coated by the hard or super hard material or withpreformed elements as described above.

[0054] An alternative method for fixing preformed hard or superhardparticles to the cutting members 4 is to place them within a drillmould. Molten drillable soft material that will eventually become thenose 5 of the drill bit 1 is then poured into the mould. On cooling themetal provides a drill bit 1 that has the hard or superhard particlesset in situ.

[0055] The present invention is inherent with significant advantages inthat the time taken for the drilling operation can be greatly reduced asthere is no need to implement complex and timely retrieval operations torecover apparatus from the bore. As a result the profitable stage ofproduction can be begin much sooner.

[0056] A further advantage, is that unlike the drill bits known to theart, the drill bit of the present invention is drillable by anotherdrill bit and the risk of damage to the second drill bit is thereforereduced. Furthermore as the cutting means of the cutting members consistof fine layers or cutting elements formed from hard material, theydisintegrate into shavings upon drilling and therefore do not act as anobstruction to any subsequent apparatus that is advanced into the well.

[0057] Further modifications and improvements may be incorporatedwithout departing from the scope of the invention herein intended.

1. A drill bit for drilling with casing in a well bore, said drill bitbeing constructed from a combination of a relatively soft material and arelatively hard material, wherein the hard material is suitable forcutting earth or rock, and wherein the combination of materials is insuch proportion and in such arrangement to allow a subsequent furtherdrill bit to drill through said drill bit.
 2. A drill bit as claimed inclaim 1 substantially constructed from the relatively soft material,wherein the relatively soft material is adapted to be drilled throughwith a standard earth drill bit.
 3. A drill bit as claimed in claim 1 orclaim 2 formed with a body having or being associated with a noseportion upon which are cutting members, wherein the body is madesubstantially from the relatively soft material and at least a leadingedge or cutting surface of each cutting member is made from therelatively hard material.
 4. A drill bit as claimed in any one of thepreceding claims, wherein the hard material is tungsten carbide.
 5. Adrill bit as claimed in any one of claims 1 to 3, wheren the hardmaterial is diamond composite.
 6. A drill bit as claimed in any one ofclaims 1 to 3, wherein the hard material is cubic boron nitride.
 7. Adrill bit as claimed in any one of the preceding claims wherein the softmaterial is aluminium.
 8. A drill bit as claimed in any one of claims 1to 6, wherein the soft material is copper or brass alloy.
 9. A drill bitas claimed in any one of the preceding claims having a plurality of softmaterials.
 10. A drill bit as claimed in any one of the preceding claimshaving a plurality of hard materials.
 11. A drill bit as claimed in anyone of the preceding claims wherein the hard material is provided as acoating.
 12. A drill bit as claimed in claim 11 wherein the coating isapplied to the nose portion.
 13. A drill bit as claimed in claim 11 orclaim 12 wherein the coating is a continuous layer or film.
 14. A drillbit as claimed in claim 11 or claim 12 wherein the coating isnon-continuous, such that surfaces of the drill bit are afforded areaswhich are not coated by the hard material, wherein upon rotation of thedrill bit, the cumulative effect of the coated areas gives completecircumferential coverage of the dimensions of the drilled well bore. 15.A drill bit as claimed in any one of the preceding claims wherein thehard material is applied to an intermediate which is amenable to thenose of the drill bit.
 16. A drill bit as claimed in claim 15 whereinthe intermediate is nickel.
 17. A drill bit as claimed in any one ofclaims 1 to 10 wherein the hard wearing material is applied to the noseas preformed elements wherein the cumulative effect of said preformedelements is to cover the surface of the nose and so act as a coatingthereof.
 18. A drill bit as claimed in claim 17 wherein the preformedelements are chips or fragments of the hard material.
 19. A drill bit asclaimed in claim 17 or 18 wherein the preformed elements are attached tothe nose by brazing.
 20. A drill bit as claimed in any one of claims 17to 19 wherein the preformed elements have a reinforced structure to aiddrilling of hard formations.
 21. A drill bit as claimed in claim 20wherein the preformed elements are pre-weakened prior to attachment tothe nose in order to allow fracture of the preformed elements upondrilling.
 22. A drill bit as claimed in any one of the preceding claimsalso comprising a plurality of flow ports to allow fluid bypass andlubrication of the bit.
 23. A drill bit as claimed in any one of thepreceding claims also comprising a stabiliser or centraliser.
 24. Adrill bit as claimed in any one of the preceding claims also comprisingreaming members.
 25. A method of fixing a hard or super hard wearingmaterial to a drill bit nose made of a soft drillable material, whereina jet is used to blow gases at very high speeds towards a cast of thenose and particles of the hard or superhard wearing material areintroduced into the gas stream, wherein the kinetic energy of theprocedure is converted to thermal energy which welds the particles tothe nose.
 26. A method for fixing a hard or superhard wearing materialto a drill bit nose made of a soft drillable material, wherein particlesof the hard or superhard wearing material are placed within a mould andthereafter the soft drillable material is poured in molten form into themould, such that on cooling said hard or superhard wearing particles areset in situ.
 27. A method for drilling a well bore comprising attachinga drill bit in accordance with any one of the preceding claims tocasing, drilling a bore through the earth formation and subsequentlyrunning a further drill bit in the well inside the casing and drillingthrough the first drill bit.